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Destructive algae returns to chemically-cleaned Finnish lake

Swimming at the lake is not recommended at the moment, despite a major purification process in 2017.

Vesiruttoa on Littoistenjärven rannoilla isoissa kasoissa.
Liitoinen lake was previously chemically cleaned, but algae is evident again Image: Kati Grönholm / Yle

Significant amounts of algae have returned to Littoinen lake in southwestern Finland, the lake's management board announced on its website, adding that visibility in the lake has dropped dramatically.

A comprehensive chemical scrub of the lake, carried out in 2017 by the Finnish Environment Institute Syke, initially appeared to remove the algae which had been monopolising oxygen in the body of water and killing off plant life and fish. The process also returned the lake to its pristine crystal clear condition, and it became a local tourist attraction.

However, later in the same year, reports began to emerge of a large number of dead fish ound in the lake.

In November 2018, the lake became overrun by waterweed, a freshwater vegetation widely regarded to be poisonous in Finland and other parts of the world.

Littoistenjärvi toukokuussa 2017.
Littoistenjärvi toukokuussa 2018.
Kemikaaleilla puhdistettu Littoistenjärvi on jo ensimmäisen vuoden aikana samentunut huomattavasti. Kuvapari on vuosilta 2017 ja 2018.

Swimming not recommended

The management board's announcement detailed how algae began to build up over the midsummer weekend, and that visibility in the water was down to half a metre in some parts. In addition to the detection of green algae, a strain of blue algae has also been found.

Johanna Mäkinen, head of the environmental health care department in the nearby municipality of Lieto, said that health supervisors are carefully monitoring the situation.

"There is a lot of blue-green algae in the lake, which is why bathing is not recommended," Mäkinen added.

The Littoinen lake management board received a 100,000-euro grant from the Ministry of the Environment in June in order to continue monitoring and analysing the effects of the chemical treatment.

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